The instant invention relates to archery bows and more specifically relates to an eccentric for use in a compound archery bow.
Compound archery bows are well known in the art. For example, U.S. Pat. No. 4,064,862 to Groner, and U.S. Pat. No. 4,201,177 to Holman are descriptive of such bows and their mode of operation. Compound archery bows are generally characterized by a pair of leveraging devices mounted at the distal ends of a pair of opposing bow limbs. The leveraging devices usually comprise a wheel or pulley and are commonly referred to as "eccentrics" because they are characteristically pivoted around an off-center axis. Eccentric devices are generally operable for providing a mechanical advantage to decrease the force required to draw the bow to a maximum draw weight. The eccentrics are pivotally mounted at the distal ends of the bow limbs and are interconnected through a rigging system comprising tension cables and a bowstring. Although numerous variations of cable and bowstring arrangements are possible, a typical arrangement consists of two tension cables each of which is anchored at some point on one of the bow limbs and stretched across the length of the bow where it is threaded around the perimeter of the eccentric carried at the end of the opposing bow limb. A bowstring commonly referred to as a central stretch connects the free ends of the tension cables together to form a continuous loop through the rigging system. The rigging system may be regarded as a specialized block-and-tackle arrangement which is operable for transferring the pulling force applied to the bowstring to deflect the bow limbs toward one another.
The eccentrics include grooves or tracks analogous to the pulley grooves in a traditional block-and-tackle assembly. Specifically, the eccentrics include a bowstring track which is arranged to alternately pay out or take up a stretch bowstring as the bow limbs are alternately flexed to a drawn position or relaxed to a braced position, and a cable track which is arranged alternately to take up a stretch of cable as the bowstring is paid out, and to pay out a stretch of cable as the bowstring is wound or taken up onto the bowstring track. It is recognized that in the operation of a compound bow the bowstring lengthens as pulling force is applied due to the fact that as the eccentrics pivot about their axis the stretches of the bowstring stored in the bowstring track are paid out. In a like manner, stretches of the tension cables are taken up or wound onto the cable tracks so that the cable decreases in length, and the tips of the bow limbs are deflected toward one another to the drawn position. The opposite phenomenon occurs when the bowstring is released and the potential energy stored in the flexed bow limbs is released and transferred into an arrow.
A conventional eccentric typically comprises a larger diameter rim portion which includes the bowstring track, a reduced diameter rim portion which includes the tension cable track, and a central hub portion which interconnects the rim portions. In this manner, each eccentric works identically to a block-and-tackle wherein a larger stretch of bowstring is paid out on the larger diameter bowstring track than the amount of tension cable taken up on the reduced diameter cable track.
Many variations of compound bow eccentrics have heretofore been available and have been operable for various purposes. For example, U.S. Pat. No. 4,337,749 to Barna; U.S. Pat. No. 4,340,025 to Caldwell; U.S. Pat. to Simonds No. 4,438,753; U.S. Pat. to Larson No. 4,686,955; U.S. Pat. to Cook et al No. 4,770,154; U.S. Pat. to Larson No. 4,774,927; U.S. Pat. to Chattin No. 4,887,582; U.S. Pat. to Kudlacek No. 4,838,236; U.S. Pat. to Larson No. 4,967,721; U.S. Pat. to Darlington No. 4,986,25 250; and U.S. Pat. to Larson No. 5,020,507 disclose various eccentric devices which represent the closest prior art to the subject invention of which the applicant is aware. The eccentric devices disclosed in these references are generally operable for adjusting or improving different aspects of eccentric and/or bow characteristics, such as degree of mechanical advantage, maximum drop-off percentage, draw weight, and draw length. In addition, many of the more advanced designs of eccentrics enable a rapid build-up of force to a peak draw weight at an intermediate draw position and thereafter have a built-in drop-off in the amount of force required to hold the bow at full draw, thus making it less strenuous to hold the bow at full draw and subsequently to take aim and fire.